The present invention relates generally to high quality factor (Q) BEOL (back end of line) inductor elements with dynamically driven, patterned, conductive shields which reduce or eliminate parasitic substrate capacitive coupling between the inductor and the conductive.
Prior art implementations for BEOL inductor elements have utilized a buffered drive of adjacent spiral inductive elements to achieve a higher quality factor (Q), and have required complicated processing or many additional accessory functional elements, such as a variable attenuator and a variable phase shifter. These prior art implementations of shielded inductors have attempted to achieve a higher Q by increasing the magnetic flux coupling of the inductor (Yeung, et. al., xe2x80x9cDesign Considerations for extremely High Q Integrated Inductors and Their Application in CMOS RF Power Amplifierxe2x80x9d, IEEE Proceedings, RAWCON, 1998).
Other prior art implementations have utilized a grounded, low impedance, patterned, conductive shield underneath the inductor to intercept the parasitic capacitive coupling between the inductor and the conductive substrate. These implementations achieve higher Q through reduction of the power loss in the conductive substrate. The capacitively coupled current that would normally flow through the conductive substrate (causing power loss and Q reduction) is shunted through a very low impedance directly to a ground potential (reducing the power loss). An example of this approach can be seen in International Patent WO 02/50848 A2, by Wu. The shield in these implementations is patterned in such a way as to reduce or eliminate the magnetically induced eddy currents that would normally flow in a shield that consisted of a large plate of conductive material. These eddy currents would reduce the net magnetic field of the inductor, reducing Q and inductance, negating any beneficial effects of the shield.
The present invention provides high Q BEOL inductor elements with dynamically driven, patterned, conductive shields. A patterned, conductive shield structure/layer is provided between the inductor element and the substrate, and the patterned shield layer is dynamically driven to the same electrical potential as the inductor element itself, to reduce or eliminate parasitic substrate capacitive coupling between the BEOL inductor element and the conductive substrate.
The shield layer is patterned to form a plurality of conductive segments which are selectively insulated from each other such that eddy currents cannot flow from one conductive segment to an adjacent conductive segment, to prevent the flow of eddy currents in the patterned shield structure when it is dynamically driven to the same electrical potential as the BEOL upper inductor element. The conductive segments are generally formed and designed to extend from the edges of the shield layer towards the center of the shield layer and the spiral inductor element, and are electrically connected together to be dynamically driven to the same electrical potential as the BEOL inductor element.
In one disclosed embodiment, the spiral inductor element is designed with a series of linear conductor segments separated by substantially 90 degree angular bends, to form a square or rectangular shape spiral, such that the series of linear conductor segments and angular bends enable the inductor element to spiral within itself and terminate in an inner end near the center of the convoluted spiral inductor element. A square or rectangular shaped patterned, conductive shield structure is formed below the spiral inductor element, between the spiral inductor element and the substrate, and is larger in area with a greater length and greater width than the spiral inductor element, such that it extends beyond the outer lateral edges of the spiral inductor element to shield the inductor element from the substrate. The patterned shield typically extends beyond the outer lateral edges of the inductor element by a distance roughly equal to, or greater than, the dielectric stack height separating the inductor element and the patterned shield.
In another disclosed embodiment, the spiral inductor element is designed with a series of linear conductor segments separated by substantially 45 degree angular bends, to form a polygon octagonal shape spiral, such that the series of linear conductor segments and angular bends enable the inductor element to spiral within itself and terminate in an inner end near the center of the convoluted spiral inductor element. A patterned, conductive shield structure is formed below the spiral inductor element, between the spiral inductor element and the substrate, and is larger in area than the area of the spiral inductor element, such that it extends beyond the outer lateral edges of the spiral inductor element to shield the inductor element from the substrate. The patterned shield typically extends beyond the outer lateral edges of the inductor element by a distance roughly equal to, or greater than, the dielectric stack height separating the inductor element and the patterned shield.
The reduction or elimination of the parasitic capacitive components provides high Q inductor elements and components. The inductor elements can achieve at least a 100% increase in peak quality factor Q using the dynamically driven patterned, conductive shield structures of the present invention.